[Brantel]

Does anyone think that ground effect could be well effecting my AOA during the flare to land?

I have done at least 50 stalls at alt in my RV7 and my Dynon AOA indicator and beeper/buzzer always indicate a stall at altitude about 1 red bar above the yellow and the progressive beeper always goes to a solid tone about right when the buffet happens. Full or no flaps, the indications are real close to the break. This tells me my calibration is dead on...at altitude!

When I land in a three point, the Dynon is still well in the yellow and the beeper is still intermittent even at touchdown. No full tone and the AOA is still in the yellow.

I would expect to hear full tone right at the point where all wheels hit the runway or sometimes I drag the tailwheel slightly before the mains and I would expect the AOA to be indicating stall at this point.

Does anyone think that ground effect will screw with the AOA of the Dynon since they take their delta readings on the pitot?

I normally hit full flaps just prior to turning base, hold 75-80kts till base to final, hit 70-75kts early final and 65-70kts on close final over the fence. The decent rate can be really high at 65kts depending on loading...my plane seems to stall at altitude right on Van's published numbers when I use TAS as the reference. IAS is lower than Van's numbers.

My AOA indicates about mid green zone on the deadly base to final turn @ 70-75kts maybe a little higher if light and maybe a little lower if heavy. +-1 bar variation.

I have been working on my short field techniques and trying to reduce my speed across the threshold. CS equiped planes really have an advantage here...seems with the FP, there is a point where you fall off the cliff on decent rate and you need some energy to arrest that at the bottom. Keeping the speed up stops this but leads to longer rollouts.

All of this has me thinking that an RV7 FP can be well on the backside of the power curve, in the area of high decent rate but still be well above the critical AOA. One of you smart engineers might explain all this...

Sorry for the ramblings, I am navigating thru one of the corners of my plane's performance envelope that is critical to short field operations and I have no intentions of wrecking me or my plane!!! I don't like the feeling of being too far on the back side of the curve since a loss of engine in this area most likely means your landing on the fence or the ILS antenna array or worse at some fields and most short ones.

 

[MikeJ 7A]

All of this has me thinking that an RV7 FP can be well on the backside of the power curve, in the area of high decent rate but still be well above the critical AOA. One of you smart engineers might explain all this...

I'm not a engineer, smart or otherwise, but AOA alone will not keep you safe in the final turn. A warning from my old T-38 manual states: "If a high sink rate condition is allowed to develop, excessive altitude loss will occur and recovery may not be possible..." In other words, it's possible to be on airspeed and on AOA but still develop a sink rate in the final turn that will kill you. VVI and throttle setting must be a part of your crosscheck.

 

[Brantel]

Yeah, I would agree...pancaking into the ground is just as bad...thus my concern for operating in this area of the envelope. Jack Roush found this out at Sloshkosh this year.

But...it will go a long ways to help prevent a base to final (or the overshoot-pullback turn) stall/spin that seems to kill allot of RV pilots and passengers!

 

[flyeyes]

The AOA should be accurate in ground effect--local flow is local flow.

I think what may be confusing you though is the three-point attitude of your RV.

AFAIK, All of the RVs sit well below stall AOA in the three-point attitude. This is certainly true of the RV-8, -4, and the -7 I flew recently.

It's easy , while under control (and not stalled) to touch the tailwheel to the runway with the mains well off the ground. If you have any vertical rate when you do this though, it results in an inelegant flop onto the runway as the tailwheel levers the back of the airplane up, reducing the wing's AOA. It's also hard on the tailwheel.

You don't really do "full stall" landings in an RV, even when three-pointing. This is not the same as many other taildraggers.

Standard disclaimer applies: I'm not an expert, and this isn't my day job

 

[Brantel]

Maybe this is why the "RV Skip" is so well known??? (and hard to prevent 100% of the time)

But really...I have my AOA progressive beeper set to start at the bottom of the yellow and it is full on at the top of the yellow or bottom of the red. It works fine at altitude when practicing stalls but in the three point flare most of the time it never comes on or it goes nuts once the plane is on the ground and starting to slow down. I do not look at the AOA in the flare so I can't see what it is doing.

My thought was that it should at least get into the yellow in a three point flare. I can see where an RV7 might not be at critical AOA in the three point but I would expect it to be somewhere in the yellow. This is why I was thinking maybe ground effect screws with the AOA sensor on the Dynon.

 

[Pmerems]

Just noticed this old post

I just noticed this old post and had the same question in my mind for the past 3 yrs.

After completing my RV-7A and calibrating my Dynon AOA I always wanted to improve my landings and want to hear some for the progressive AOA beeps prior to touchdown. Sometimes I get them and sometimes I don't. It became an obsession, just ask my wife. When I return from flying she would ask "did you get your beeps."

So since I work in the defense industry and with lots of very smart Aero engineers I decided to ask the same question, "Does ground effect influence the accuracy of the low wing pitot mounted AOA system". The result was a lot of head scratching and "thats a very good question" but no deffinative answer.

So have I been chasing my "phantom" beeps all these years? I believe so. My landing are great (not perfect nor as slow as I would like at times), but I rarely get my AOA beeps on landing.

So my conclusion is that ground effect has some influence on the pitot mounted AOA system.

Disclaimer: Your milage may vary